In conventional permanent magnet motors, the rotor comprises a plurality of permanent magnets are carried by a rotor body and arranged so that magnetic poles are formed. The rotor is driven by electrified stator-side coils that are disposed substantially around the rotor thereby forming rotating magnetic fields. Due to the permanent magnets, magnetic fields are formed individually for the predetermined poles, so that the motor size can be reduced and the motor output can be increased.
In the prior art, the rotor permanent magnets have been rectangularly shaped and adhesively secured to the outside of the rotor body and supported against centripetal load by a hoop fit over the rotor periphery. Other arrangements include rectangular magnets fit into closed slots within the rotor body near the rotor surface.
U.S. Pat. No. 4,242,610 describes an arrangement wherein wedge-shaped permanent magnets are carried by a rotor body. The rotor body includes wedge shaped slots which hold the magnets. The magnets are shorter in length than the slots. The outer surface of the magnets is flush with the cylindrical outside surface of the rotor body. A hoop is fit over the outside surface of the magnets to assist in retaining the magnets. This arrangement requires the rotor body and the magnets to be ground to precise dimension and a hoop to be heat shrunk around a perimeter of the rotor body.
The present inventors have recognized the desirability of providing a permanent magnet rotor construction that reduced manufacturing time and cost and which increased operating reliability of the rotor.